first could be a tube worm or could be an anemone of some type... possibly apistaisa but its a really bad picture so i wouldn't say anything for sure uless you can post a better picture, possibley from the side to get a profile on it
ummm third is a tube worm... aka good
forth no idea... macro algea of some type keep an eye on it as they can be a problem if they get out of control...
I have a few of those popping up on one rock. I also have another anemone that is on a diff rock but looks completely different. I'll see if I can get a pic
Tanks over run with aiptasia are usually a sign of excess nutrients and subpar water quality. I do agree you should get rid of the aiptasia though because it is stinging celled and will harm other inhabitants and spread. Good luck killing it however. Just get a peppermint shrimp or two. They knock em out quick.